The use of soap as a cleaning agent goes back to the dawn of civilization and has had a long record of safety and efficacy. When used as a detergent, soap has two important drawbacks; its poor solubility in cold water and insolubility in water of the calcium and magnesium salts. In an effort to remove these drawbacks, the detergent industry has shifted away from soap and has adopted various synthetic surfactants as the active ingredients in its detergent compositions.
It is well known that in hart water, insoluble soaps are formed which tend to flocculate to form what is called lime scum or lime soap. This tends to be deposited on either the fabrics which have been washed or on vessels in which washing and rinsing is carried out.
In fabrics, the common laundry soils generally consist of about 40% by weight particulate soil and about 60% by weight of oily soil from human sebum or perspiration. The particulate soil component of the laundry soils is mainly composed of abut 75% clay and silica, and about 20% lime soaps. Since lime soaps are generally not efficiently removed by the surfactant in the detergent composition nor are they sequestered by sodium tripolyphosphate or other similar material, which can also be present in the detergent composition, the net result is the cumulative build-up of lime soap deposits on washed fabrics. This condition leads to gradual "graying-up" of washed fabrics and to rancid odors of the fabrics which comes from enzymatic decay of the unsaturated fatty acid portion of lime soaps.
Lime scum can deposit on vessels in which washing and rinsing is carried out to form what is known as "bath tub ring".
More than thirty years ago, it was discovered that precipitation of lime soap could be prevented through the addition of lime soap dispersing agents to the soap. These formulations, however, contained sodium pyrophosphate, which was found to be deleterious to the environment due to the phenomenon called eutrophication, or simply, excessive algae growth in bodies of water into which the used wash liquor containing phosphate is discharged.
Lime soap or lime scum is essentially insoluble calcium salts of fatty acids which are in the form of large aggregates of about 0.01 to 0.03 cm or 100 to 300 microns in size. Such aggregates are not effectively dispersed by the surfactants commonly used in detergent formulations. When a lime soap dispersant is present in a detergent composition, it breaks down or disperses the large-sized lime soap aggregates to micron or even sub-micron particles resulting in a milky dispersion. Thus, the presence of a lime soap dispersant in a detergent composition permits flushing or rinsing away of the lime soap with the result that deposition of lime scum on fabrics is reduced or eliminated and formation of bath-tub rings can be prevented.
The lime soap dispersants, therefore, function to prevent formation of insoluble lime soaps or prevent such soaps from flocculating so that they can be flushed away with the washing or rinsing water and do not adhere to fabrics or to surfaces of the washing vessels.
U.S. Pat. No. 3,692,704 discloses detergent compositions comprising about 50% detergent and about 50% detergent builder wherein the builder component consists of 60% by weight sodium polyacrylate of Mw 100,000 and 40% by weight of poly (N,N-dicarboxymethyl acrylamide) of Mw 50,000.